President Donald Trump addresses the Conservative Political Action Conference on Feb 23. His steel and aluminum tariffs will take effect March 23. (Tom Williams/CQ Roll Call)

Updated at 4:22 p.m. | President Donald Trump on Thursday set in motion tariffs that will slap fees on many imports of steel and aluminum, moving ahead with a major part of his “America first” philosophy above the loud objections of Republican lawmakers.

“People are starting to realize how important it is,” Trump said just before signing in the Roosevelt Room. He said a “strong steel and aluminum industry” is “absolutely vital” for national security, predicting his action will trigger the reopening of American production facilities.

The upcoming resignation of British Prime Minister David Cameron, seen during a visit to the Capitol in 2013, is just one consequence of the Brexit vote. (Tom Williams/CQ Roll Call file photo)

The shock waves of the decision by British voters to leave the European Union began almost immediately after the polling booths closed Thursday night. The British pound plummeted against the dollar, the Dow tanked , and experts predicted years of uncertainty in the United Kingdom and Europe. Here are five immediate takeaways.

1. Economic instability : Economic forecasts predicted a prolonged recession in Europe and the United Kingdom after a Brexit vote. Sebastian Mallaby, a senior fellow at the Council on Foreign Relations, explained why in an op-ed published last week in The Washington Post: British regulations, derived from EU rules, will have to be rewritten wholesale. Nobody will know for some time what will happen with Britain's commercial relationships with its trading partners or its membership in the EU single market. Global businesses based in London will begin considering whether they should move, triggering a potential real estate bust — and anyone who lived through the 2008 recession knows what that would mean for consumer spending.